How do I add details to my App Store refund request?

There is no location to add additional information. It is actually quite simple, you agree to the charges when you double click the side button with that amount showing on the screen, followed by verification that they were made by you with FaceID or Passcode. In most cases all transactions in the App Store are final, but at times Apple may provide a compassionate refund. It should never be expected though.

It makes no difference if you use the service or not. That is true for other services as well, such as Netflix where you will still pay the subscription price whether you watch any of the shows or not. Cancelling the subscription is what is needed to prevent future charges.

While you can contact Apple directly here, the previous post by tubesarmey appears to be simply an AI response from someone that typed in your question to a service like ChatGPT and there is absolutely no process to expedite your claim or guarantee you will get the refund. Those types of post are simply unhelpful and not factual.

Contact Apple Support - Apple Support